The invention relates to a power transmission device for transmitting rotation by gears and a sheet feeding apparatus having a power transmission device.
A power transmission device that transmits a continuous rotary movement through dividing it into rotary movements of a definite angle using an intermittent gear is used in a sheet feeding apparatus for conveying a sheet of paper.
For example, in the publication of the unexamined patent application 2002-265076, it is disclosed a sheet feeding apparatus which conveys out sheets of paper one by one by a process such that, by the combination of a driving gear with a follower gear made up of an intermittent gear, a continuous rotary movement of the driving gear is converted into followed rotations of a definite angle, which are transmitted to the follower gear, and the rotary movements of a definite angle of the follower gear are transmitted to sheet feed rollers.
In such a power transmission device, there is a problem that, because of shocks generated every time when the meshing of the gears transfers from a toothless state to a mesh state, shock sounds and wear or breakage of the gear teeth are generated.
For a countermeasure of this, it has heretofore been put into practice to provide a shock absorbing elastic member at the meshing portion.
Further, in the publication of the unexamined patent application 2002-265076, the generation of abnormal sounds and the breakage of the gear are prevented by making the shape of teeth of the follower gear such one as to be capable of reducing the pressing force at the time of meshing of the gears.
As regards the means in which an elastic member is provided, there are a problem that the number of parts increases which results in a high cost and a low durability of the device, a problem that the low durability of the elastic member causes the durability of the device to be lowered, a problem that it is difficult to fit a small gear with an elastic member, etc.
In the publication of the unexamined patent application 2002-265076, by the use of a means in which a notched slope is formed at the first tooth and the second tooth adjacent to a toothless portion at its downstream side in an intermittent gear, the abnormal sounds and the breakage of teeth are prevented. Because such a prevention means is to lower the strength of the teeth, it is insufficient for the prevention of the breakage of teeth, and the problem that a breakage of teeth occurs, for example, in a case where the torque of the drive force to be transmitted is large cannot be solved. Further, the means is insufficient for the prevention of the shock sound generated at the start of meshing.
That is, at the time of transition into meshing from a toothless portion, also in a gear device described in the publication of the unexamined patent application 2002-265076, because the transition into a mesh state is made at the same time over the whole length of a tooth in the axial direction, the shock is large, and a shock sound is generated.
As described above, the gear device in the publication of the unexamined patent application 2002-265076 is insufficient for both the purposes of the prevention of a shock sound and the prevention of a breakage of teeth.